1. Field of the Invention
This invention relates to copolymers of maleic anhydride (MAN) and a C.sub.1 -C.sub.4 alkyl vinyl ether (AVE), and, more particularly, to solvent-free, fine white powders of such copolymers having advantageously high molecular weights and without taste or odor, for use in oral care products, particularly denture adhesives, and to a solvent-free process for making such copolymers.
2. Detailed Description of the Prior Art
British Pat. 906,230 described the preparation of copolymers of maleic anhydride and methyl vinyl ether in benzene as solvent. Example 1 also disclosed a copolymerization process in absence of solvent in which powdered maleic anhydride, methyl vinyl ether and initiator were precharged into an autoclave and reacted at 55.degree. C. The specific viscosity (SV) of the product, however, was only 3.45 (1% in methyl ethyl ketone, MEK).
U.S. Pat. No. 5,047,490 described a polymerization process substantially the same as Example 1 of British 906,230. However, the reference does not disclose any procedure for separation of remaining traces of MVE from the product, other than distilling off the MVE from the reactor. Accordingly, such polymers inevitably carry a bad taste and odor which is unacceptable for oral care products such as denture adhesives. Furthermore, the SV of the polymers obtained therein was only 2 to 5.
Accordingly, it is an object of this invention to provide a solvent-free process for making high molecular weight copolymers of MAN and an AVE, particularly having an SV of &gt;6, and which are without taste or odor, so that they can be used advantageously in commercial oral care products such as denture adhesives.
These and other objects and features of the invention will be made apparent from the following more particular description of the invention.